1. Field of the Invention
The present invention relates to a highly weather-resistant copolymer, a process for producing the same, and a coating composition made from the same. More particularly, it is concerned with a copolymer useful as a coating material, ink, adhesive, fiber treatment, and the like, and also with a coating composition made from said copolymer which forms a coating film having not only longlasting good weather resistance but also good drying property, good gloss, good buildability, and good solvent resistance.
2. Description of the Prior Art
Among important coating materials is acrylic resin and methacrylic resin (which are collectively referred to as (meth)acrylic resin hereinafter). The typical uses of (meth)acrylic resin in the coating area are as lacquers and curable coating materials. Lacquers are commonly used for the coating of building materials, wood products, and plastics products because of their easy usage. All required for lacquer coating is to apply a lacquer as such to a substrate and let it dry. Curable coating materials are a composition composed of an acrylic polyol and a crosslinking agent. The acrylic polyol is produced by copolymerizing hydroxyl group-containing monomers such as hydroxyethyl (meth)acrylate with other monomers. The crosslinking agent is a polyisocyanate compound or aminoplast resin. The curable compositions are either of room temperature-curable type or thermosetting type. The coating materials based on the curable resin composition are used for automobiles, home appliances, steel machines, building materials and so on because of their better durability compared with the above-mentioned lacquers.
The coating resin compositions used in the application areas where the coating film with a good-looking appearance is required are usually based on a copolymer containing 30-60 wt % of aromatic curable monomer to impart good gloss, buildability, solvent resistance, and chemical resistance. Unfortunately, the resin composition based on a copolymer containing a large amount of aromatic monomer provides a coating film which is poor in weather resistance, and consequently it is incorporated with an ultraviolet stabilizer or ultraviolet absorber so that it can be put to practical use, especially under sever condition.
There has recently been proposed the use of an ultraviolet absorbing vinyl monomer (as a comonomer) in place of the externally added ultraviolet stabilizer or absorber. (See Japanese Patent Publication No. 42751/1986.) This new technology is effective in improving the weather resistance of the composition to some extent, but is not satisfactory when it comes to long term weather resistance.
Unfortunately, the coating resin composition having the improved weather resistance resulting from the incorporation of an ultraviolet stabilizer or absorber in the absence of aromatic vinyl monomer or by in the absence of aromatic vinyl monomer the copolymerization with an ultraviolet absorbing monomer does not necessarily provide a coating film with good gloss, buildability, and appearance.